1. Field of the Invention
The present invention relates to an optical switch using an electro-acoustic effect, which is a high speed A/O switch with a large extinction ratio.
2. Description of the Background Art
an optical switch using an electro-acoustic effect has been utilized for a variety of purposes such as a submarine cable switching and an optical signal processing, and is particularly useful for a light blocking at a time of optical path switching.
The optical switch is constructed by using a diffraction grating, which in turn is formed by an electric acousto-optic element made of a monocrystal PbMoO.sub.4 for example, to which ultrasonic waves are applied in order to periodically change the refractive index of the acousto-optic element and thereby make the electric acousto-optic element functioning as the diffraction grating.
However, the conventional optical switch has a large insertion loss polarization dependency of about 0.5 dB for example, and a large polarization mode dispersion of about 10 ps delay for example, so that the conventional optical switch has been associated with a problem that the waveform deformation is caused for the high speed signals in random polarization states, as well as a problem that the frequency of the light is shifted as the light passes through the optical switch.